The present invention relates to a ferromagnetic material sputtering target used for depositing a magnetic material thin film for a magnetic recording medium, in particular, a granular magnetic recording layer, and to an Fe—Pt-based ferromagnetic material sputtering target showing low particle generation.
In the field of magnetic recording represented by hard disk drives, ferromagnetic metal materials, i.e., Co, Fe, or Ni-based materials are used as materials of magnetic thin films that perform recording. For example, in recording layers of hard disks employing a longitudinal magnetic recording system, Co—Cr or Co—Cr—Pt ferromagnetic alloys of which main component is Co are used.
In recording layers of hard disks employing a perpendicular magnetic recording system that has been recently applied to practical use, composite materials composed of a Co—Cr—Pt ferromagnetic alloy, of which main component is Co, and a nonmagnetic inorganic grain are widely used. In many cases, the magnetic thin film of a magnetic recording medium such as a hard disk is produced by sputtering a ferromagnetic material sputtering target consisting primarily of the above-mentioned material because of its high productivity.
Meanwhile, a recording density of a magnetic recording medium is rapidly increasing every year, and the current surface density of 100 Gbits/in2 may reach 1 Tbits/in2 in the future.
If a recording density reaches 1 Tbits/in2, the size of a recording bit is smaller than 10 nm. In that case, it is expected that superparamagnetism due to thermal fluctuation will pose a problem. It is also expected that magnetic recording media currently used, for example, a material in which magnetocrystalline anisotropy is enhanced by adding Pt to a Co—Cr based alloy, or a material in which magnetic coupling between magnetic grains is weakened by further adding B thereto, will not be sufficient.
This is because a grain with a size of 10 nm or less stably showing a ferromagnetic behavior is required to have higher magnetocrystalline anisotropy.
In view of the discussion above, an FePt phase having a L10 structure gathers much attention as a material for an ultrahigh-density recording medium. An FePt phase having a L10 structure is also a potential material suitably applicable to a recording medium because it has an excellent corrosion resistance and oxidation resistance.
In order to use an FePt phase as a material for an ultrahigh-density recording medium, a technology is required to be developed where ordered FePt nanograins are dispersed in a similar orientation and in a magnetically isolated manner as high densely as possible.
From this point of view, a granular magnetic recording medium has been proposed. This granular medium, which has a structure where magnetic fine grains are deposited in a nonmagnetic matrix such as an oxide, needs to further have a structure where the magnetic grains are magnetically insulated mutually through the intervention of a nonmagnetic substance. For the granular magnetic recording medium and known Documents related to it, see Documents such as Patent Document 1, Patent Document 2, Patent Document 3 and Patent Document 4.
Moreover, the magnetic recording layer is composed of a magnetic phase such as an Fe—Pt alloy, and a non-magnetic phase to isolate the magnetic phase, and a metal oxide is effective as one of the materials for the non-magnetic phase. Many of these magnetic recording layers are formed by the sputtering deposition method. When trying to sputter a ferromagnetic material sputtering target containing a metal oxide using a magnetron sputtering apparatus, a problem may arise in general such an inadvertent release of the metal oxide during sputtering and abnormal electrical discharge starting at a void inherently included in the target, resulting in particle generation (dust adhered on a substrate).
In order to solve this problem, the adherence between a metal oxide and a matrix alloy is required to be enhanced, and in addition, a sputtering target is required to be more densified.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2000-306228
Patent Document 2: Japanese Laid-Open Patent Publication No: 2000-311329
Patent Document 3: Japanese Laid-Open Patent Publication No. 2008-59733
Patent Document 4: Japanese Laid-Open Patent Publication No. 2008-169464